A web of material, such as paper produced in a paper machine, is wound into large rolls having diameters and lengths of up to several meters, for example, 3 meters wide by 10 meters long. When wound, the paper has a temperature of between 40.degree. C. (104.degree. F.) and 70.degree. C. (158.degree. F.) and a particular moisture level. Prior to further processing, such as glaze finishing in an off-line calender which in this example serves as the processing station, the roll of paper normally cools off to ambient temperature, but not uniformly over the roll's entire cross section. Rather, the cooling-off process begins at the outer layers and end surfaces of the roll and gradually progresses to the inside. Thus, a temperature gradient is created in the roll which extends primarily in radial fashion from the inside to the outside and also contains components in the roll's axial direction.
The trend toward faster throughput of rolls in a paper mill prevents one from waiting until the temperature of the roll is perfectly uniform. Instead, after a relatively short period of time, the roll is moved to the next processing step, such as the aforementioned glaze finishing. At that point, the web of paper is fed under pressure through at least one roller gap. Typically, one of the rollers forming the roller gap is heated by a liquid positioned within the roller.
The temperature gradient across the roll's radius causes a continuous temperature change of the web as it is fed into the calender. As a result, the roll's temperature increases as the paper is unrolled. Since the surface temperature of the heated calender rollers is kept constant, the glaze finish will vary over the length of the paper web. A similar phenomenon, although not as severe, occurs in the direction perpendicular to the paper web. Occasionally, different finishing effects occur along the web's edges which cool more rapidly than the center section and have to be rectified by other methods.